Fogell DJ et al. (2013), Mind the gaps: investigating the cause of the c...

XB-ART-47860

PeerJ 2013 Sep 26;1:e166. doi: 10.7717/peerj.166.

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Mind the gaps: investigating the cause of the current range disjunction in the Cape Platanna, Xenopus gilli (Anura: Pipidae).

Fogell DJ , Tolley KA , Measey GJ .

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Low-lying areas of the Cape at Africa's south-westernmost tip have undergone dramatic marine-remodelling, with regular changes in sea-level following glacial cycles. Species for which marine barriers are impenetrable underwent concomitant radical distribution changes which may account for current range disjunctions. The Cape platanna, Xenopus gilli, is a frog distributed in only three disjunt areas within low-lying regions of the southwestern Cape. We determined the relationship between frogs from these three disjunct areas, by using a combination of morphometric analysis and mtDNA (ND2 and 16S fragments) sequences of 130 frogs from eight ponds. Coalescent analyses on molecular data dated the divergence in two major clades to around 4.6 Mya, a period during which major uplifting on the eastern side of the subcontinent caused climate changes throughout southern Africa. Principal components analysis showed significant morphometric differences between each clade on head and limb measurements. Consistent differences in ventral colouration and patterning were also observed. We report on increased levels of hybridisation with X. laevis throughout the range of X. gilli, which reaches at least 27% hybrids in some ponds. Urgent conservation actions are required to control habitat loss from alien invasive vegetation, and prevent introgression with the domestic-exotic, X. laevis.

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Species referenced: Xenopus laevis
Genes referenced: tbx2

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	Figure 1. Xenopus gilli sites in the southwest of South Africa.(A) Sampling sites for the present study, squares indicate where Xenopus gilli was sampled for this study. A triangle denotes an introduced population (Measey & de Villiers, 2011), and the white filled circle the presumed type locality: Silvermine River. Note that the squares are distributed in three disjunct areas at the end of the Cape Peninsula near the towns of Kleinmond and Pearly Beach. (B) Vegetation types (after Mucina & Rutherford, 2006) and their projection onto the exposed Agulhas bank after a 120 m reduction in sea level (current coastline is shown as a black line) following Compton (2011). Note that current and historical sites for X. gilli (circles) are associated with lowland Sand-stone fynbos (blue) and not with Sand fynbos (yellow), Renosterveld (brown) or Strandveld (green). (C) Relief map of the same southwestern Cape region after a 25 m increase in sea level. Note that the Cape peninsula becomes two islands separated from the mainland by inundation of the Cape Flats. X. gilli sites in Betty’s Bay and Kleinmond are separated from those at Pearly Beach by high ground and a salt-water estuary.
	Figure 2. A network of ND2 haplotypes for Xenopus gilli populations.(A) Median-joining network diagrams of the number and structure of X. gilli haplotypes in the Cape peninsula and eastern populations based on ND2. Cape peninsula animals are indicated in grey, Pearly Beach indicated in white and Kleinmond in black. Circles are proportional to the number of individuals sequenced belonging to each haplotype and lines represent the number of nucleotide base pair changes from one to the other. Note that the 74 base pair changes between the two haplotype groups are represented by a broken line. The arrow points at a haplotype not included in the analysis but found on the Cape peninsula. (B) Pairwise difference and frequency for ND2 haplotypes for Xenopus gilli from the Cape peninsula, and (C) Pearly Beach and Kleinmond.
	Figure 3. IMa2 coalescent analysis of Xenopus gilli.Result of the coalescent analysis (in IMa2) provides histories for the three disjunct areas sampled which are represented as boxes (for sampled and ancestral populations), horizontal lines (for splitting times). The size of the boxes on the horizontal axis is proportional to estimated current and ancestral population sizes. Time is represented on the vertical axis, with the sampled sites at the top representing the sampling time. Estimated error is shown in grey (boxes and arrows).
	Figure 4. Morphometric differences between genetically defined populations of Xenopus gilli.Notched box and whisker plots display the direction of significantly different head measurements between sites identified by genetic differences (CP: Cape peninsula and (A) Agulhas plain sites Pearly Beach and Kleinmond). All plots are corrected for size and therefore based on residuals of each measurement on body length (SVL). (A) Head length (HL), (B) head width (HW) and (C) head height (HH) are all significantly different between sites (p < 0.001). (D) Values for principle component 1 also show significant differences. When notches do not overlap, there is ‘strong evidence’ that their medians differ (Chambers et al., 1983).

References [+] :

Bandelt, Median-joining networks for inferring intraspecific phylogenies. 1999, Pubmed